The present invention relates to a color cathode ray tube such as a TV, a monitor, or the like, and particularly to a cathode ray tube apparatus which realizes a flat screen using a press-molded mask for selecting colors.
In general, a cathode ray tube apparatus comprises a vacuum envelope which includes a panel having a substantially rectangular display portion, a funnel connected continuously to the panel, and a cylindrical neck connected continuously to the small diameter end of the funnel. A deflection yoke is installed thereon from the end portion of the neck on the funnel side to the small diameter portion of the funnel.
A phosphor screen having a dotted or striped three-color phosphor layer which radiates in blue, green, and red is formed on the inner surface of the panel. Also, a shadow mask (for selecting color) having a surface which faces the phosphor screen and has a number of electron beam passage apertures formed at a predetermined layout pitch is arranged to face the phosphor screen. Further, an electron gun which emits three electron beams is provided inside the neck.
In the cathode ray tube apparatus described above, the electron beams emitted from the electron gun are deflected in the horizontal and vertical directions by horizontal and vertical magnetic fields generated by the deflection yoke, so the phosphor screen is scanned horizontally and vertically through the shadow mask thereby displaying a color image.
At present, as a color cathode ray tube apparatus of this kind, a color cathode ray tube of self-convergence inline type is used widely. This apparatus adopts an electron gun of inline type which emits three-electron beams consisting of a center beam and a pair of side beams which are arranged in line and run on the same horizontal plane. The horizontal deflection magnetic field generated by the deflection yoke is arranged in a pin-cushion shape while the vertical deflection magnetic field is arranged in a barrel shape, and the three electron beams arranged in line are deflected by these horizontal and vertical deflection magnetic fields. In this manner, the three electron beams can be converged over the entire screen without requiring any special correction means.
In recent years, there has been a strong demand for flatness of the screen in this kind of color cathode ray tube. In order to achieve this flatness, it is necessary to flatten the panel. However, if the panel is flattened, the shadow mask must also be flattened. As a result, the following problem arises.
In general, in a color cathode ray tube apparatus, three electron beams are converged on the center of a phosphor screen mainly by a purity convergence magnet attached to the deflection yoke in the neck side. The three electron beams pass through the electron beam passage apertures of the shadow mask at a predetermined angle and respectively land on predetermined phosphor layers. To optimize landing margins thereof in relation to the phosphor layers, it is necessary to set optimally the distance between the inner surface of the panel and the shadow mask.
Where q is the distance in the tube-axis direction between the shadow mask and the inner surface of the panel, "sgr" is the distance between the center beam 3G and each of the pair of side beams 3B and 3R on the inner surface of the panel, and Ph is the pitch of the landing position of the center beam 3G in the in-line direction of the three electron beams on the inner surface of the panel, "sgr" and Ph must be substantially constant over the entire surface of the phosphor screen in order to attain uniformness of the screen resolution. Consequently, if the panel is flattened, the shadow mask must also be flattened so that q is substantially constant, in order to make "sgr" and Ph substantially constant on the entire phosphor screen.
In general, however, the shadow mask is manufactured by shaping a shadow mask material, which has a flat thin-plate-like shape and electron beam passage apertures formed by photo-etching, into a predetermined curved surface. This shaping is carried out in a manner that the non-aperture portion of the mask material which surrounds a region where electron beam passage apertures are formed is clamped and fixed by a die and a Planck holder and the aperture-formed region is bulged by a punch and a knockout. Therefore, if the shadow mask is flattened and the amount of an extension caused by the bulging is reduced, sufficient plastic deformation cannot be obtained and the mask material therefore cannot be shaped into a predetermined curved surface. Also, the shaping strength of the shadow mask is deteriorated to cause deformation easily.
As a measure for solving this problem, between the phosphor screen and the cathode of the electron gun which emits three electron beams 3B, 3G, and 3R arranged in line to the phosphor screen, there are provided two orbital correction means by which the force for correcting the pair of side beams 3B and 3R toward the center beam 3G is changed between the center and the peripheral portion of the phosphor screen are provided. As a result of this, the virtual distance Sg between the center beam 3G and each of the side beams 3B and 3R in the in-line direction of the three electron beams between the center and the peripheral portion of the phosphor screen varies such that the virtual distance Sgc1 when the electron beams run toward the peripheral portion is smaller compared with the virtual distance Sgc0 when the beams run toward the center of the screen.
These two orbital correction means are arranged such that generated forces Fr0 and Ff0 are set to zero with respect to three electron beams 3B, 3G, and 3R running toward the center of the phosphor screen and the side beams 3B and 3R are over-converged by means of a force Fr1 generated by the neck-side orbital correction means with respect to three electron beams 3B, 3G, and 3R running toward the peripheral portion. Further, the side beams 3B and 3R are under-converged by means of a force Ff1 generated by the panel-side orbital correction means.
As a result of this, the virtual distance Sg at the cathode decreases from Sgc0 at the center of the phosphor screen to the Sgc1 at the periphery thereof, so that the distance q between the inner surface of the panel and the shadow mask in the tube-axis direction at the peripheral portion of the phosphor screen can be increased by xcex94q=qxe2x88x92q0 in relation to the distance q0 between the inner surface of the panel and the shadow mask in the tube-axis direction at the center of the phosphor screen.
However, if there are provided orbital correction means for over/under-converging the pair of side beams 3B and 3R in correspondence with the position of the phosphor screen, as described above, a problem arises in that the convergence characteristic of the three electron beams 3B, 3G, and 3R is deteriorated as the amount of the orbital correction increases.
The present invention has been made in view of the above problem, and its object is to provide a color cathode ray tube apparatus which is capable of improving the convergence characteristic of three electron beams over the entire phosphor screen even if a flat panel is combined with a shadow mask shaped to have a curved surface which is hardly deteriorated in processability and shaping strength.
To achieve the above object, a color cathode ray tube apparatus according to the present invention comprises: a vacuum envelope including a substantially rectangular panel having first and second axes which pass through a tube axis and are perpendicular to each other, a funnel connected to the panel, and a neck connected to an end of a small diameter portion of the funnel. Additionally, the color cathode ray tube comprises a phosphor screen formed on an inner surface of the panel; a mask for selecting colors, the mask having a surface which faces the phosphor screen with a predetermined distance, and a number of electron beam passage apertures formed in the surface. The color cathode ray tube further comprises an electron gun arranged in the neck for emitting three electron beams toward the phosphor screen, the three electron beams including a center beam and a pair of side beams and being arranged in line with the first axis set as an in-line direction. Further, the color cathode ray tube comprises a deflection yoke installed on the small diameter portion of the funnel and the neck and having deflection coils for deflecting the three electron beans in directions of the first and second axes and a magnetic core provided outside the deflection coils. The color cathode ray tube also comprises neck-side orbital correction means arranged between a cathode of the electron gun and the phosphor screen, for relatively over-converging the pair of side beams running toward a peripheral portion of the phosphor screen in relation to the pair of side beams running toward a center of the phosphor screen. The color cathode ray tube additionally comprises panel-side orbital correction means arranged between the neck-side orbital correction means and the phosphor screen, for relatively under-converging the pair of side beams running toward the peripheral portion of the phosphor screen in relation to the pair of side beams running toward the center of the phosphor screen, wherein the panel-side orbital correction means includes looped orbital correction coils each wound a plurality of time and arranged at four positions inside the magnetic core, and a current supply circuit for supplying the orbital correction coils with a current which is supplied to the deflection coil for deflecting the three electron beams in the direction of the second axis. In a cross section perpendicular to the tube axis at a position near the phosphor screen, each of the orbital correction coils provided between the first and second axes includes first coil wires which have an angle of 10 to 30xc2x0 with respect to the second axis and through which a current flows in a direction from a side of the neck toward the panel, and second coil wires which have an angle of 60 to 90xc2x0 with respect to the second axis and through which a current flows in a direction from a side of the panel toward the neck.
In the cathode ray tube apparatus according to the present invention, the neck-side orbital correction means includes coils arranged on the neck side of the deflection yoke, and a current supply circuit for supplying the coils with a current synchronized with a line deflection frequency.
Also, according to the present invention, the neck-side orbital correction means includes component members forming a part of the electron gun, and a voltage supply circuit for supplying the component members with a voltage.
Further, another color cathode ray tube apparatus according to the present invention comprises: a vacuum envelope including a substantially rectangular panel having first and second axes which pass through a tube axis and are perpendicular to each other, a funnel connected to the panel, and a neck connected to an end of small diameter portion of the funnel. The color cathode ray tube also comprises a phosphor screen formed on an inner surface of the panel; a mask for selecting colors, the mask having a surface which faces the phosphor screen with a predetermined distance, and a number of electron beam passage apertures formed in the surface. Additionally, the color cathode ray tube comprises an electron gun arranged in the neck for emitting three electron beams toward the phosphor screen, the three electron beams including a center beam and a pair of side beams and being arranged in line with the first axis set as an in-line direction. The color cathode ray tube also comprises, a deflection yoke installed on the small diameter portion of the funnel and the neck and having deflection coils for deflecting the three electron beams in directions of the first and second axes and a magnetic core provided outside, the deflection coils. Further, the color cathode ray tube comprises neck-side orbital correction means arranged between a cathode of the electron gun and the phosphor screen, for relatively over-converging the pair of side beams running toward a peripheral portion of the phosphor screen in relation to the pair of side beams running toward a center of the phosphor screen; and panel-side orbital correction means arranged between the neck-side orbital correction means and the phosphor screen, for relatively under-converging the pair of side beams running toward the peripheral portion of the phosphor screen in relation to the pair of side beams running toward the center of the phosphor screen, such that a convergence error amount of the three electron beams on the phosphor screen caused by the neck-side orbital correction means is canceled and reduced to 1.5 mm or less. Additionally, the deflection coils have a wind distribution adjusted so as to compensate for a remaining portion of the convergence error amount.
According to the cathode ray tube apparatus constructed as described above, the convergence characteristics of the three electron beams can be improved to be excellent over the entire phosphor screen even if a flat screen is realized by providing two orbital correction means and by using a shadow mask having a large curvature relative to the flat panel.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.